Hard surface cleaners continuously evolve and adapt to customer demands, changing times, and increasingly strict health and environmental regulations. Successful hard surface cleaners can remove greasy dirt from smooth or highly polished surfaces and disinfect them without leaving behind noticeable films or streaks. Modern aqueous cleaners typically include one or more surfactants in addition to water. Commonly, the cleaners include a small proportion of low-toxicity organic solvent(s), antimicrobial agents, buffers, sequestering agents, builders, bleaching agents, hydrotropes, perfumes or fragrances, and other components.
Hard surface cleaners designed to clean greasy soils are normally formulated at alkaline pH, typically at or above pH 10, because alkaline pH is known to work better for removing greasy dirt. Formulators would welcome cleaners that work at a more neutral pH in the range of 6 to 9 because such low-alkalinity products will be less hazardous to use and may be better for the environment. For examples of “neutral” hard surface cleaners, see U.S. Pat. No. 5,990,064 (amine oxide surfactant), U.S. Pat. No. 5,403,515 (magnesium alkyl sulfates and a nonionic surfactant), and U.S. Pat. Appl. Publ. No. 2010/0055198 (alcohols and hydrogen peroxide).
Alkalinity is considered especially important when greasy soils are baked on a surface, such as the inside surface of an oven or a grill. Cleaners for such baked-on soils typically include an alkali metal hydroxide as a principal component. Ideally, cleaners could be developed that effectively remove baked-on soils yet are formulated at relatively neutral pH so they are less corrosive and easier to handle safely.
Fatty N,N-dialkylamides have been used in cleaners but typically in industrial applications such as solvent-based degreasers for cleaning metal parts during manufacture. In one recent example (see U.S. Pat. Appl. Publ. No. 2011/0192421), the solvent-based degreaser comprises an alkyl dimethyl amide where the alkyl group has from 2 to 56 carbons.
Foaming light-duty liquid detergents containing fatty N,N-dialkylamides have been described (see PCT Int. Publ. No. WO 2011/075642). The compositions include an anionic surfactant and a foam-stabilizing surfactant (typically an amine oxide) in addition to water and the N,N-dialkylamide. Hard surface cleaners are also disclosed. This is a rare example of the use of fatty N,N-dialkylamides in a mostly aqueous composition. The reference contains no teachings regarding any advantage of using monounsaturated N,N-dialkylamides and is silent regarding any impact of pH on performance.
Fatty N,N-dialkylamides can be made by derivatizing esters or acids generated from hydrolysis or transesterification of triglycerides, which are typically animal or vegetable fats. Consequently, the fatty portion of the acid or ester will typically have 6-22 carbons with a mixture of saturated and internally unsaturated chains. Depending on source, the fatty acid or ester often has a preponderance of C16 to C22 component. For instance, methanolysis of soybean oil provides the saturated methyl esters of palmitic (C16) and stearic (C18) acids and the unsaturated methyl esters of oleic (C18 monounsaturated), linoleic (C18 di-unsaturated), and α-linolenic (C18 tri-unsaturated) acids. These materials are generally less than completely satisfactory, however, because compounds having such large carbon chains can behave functionally as soil under some cleaning conditions.
Improvements in metathesis catalysts (see J. C. Mol, Green Chem. 4 (2002) 5) provide an opportunity to generate reduced chain length, monounsaturated feedstocks, which are valuable for making detergents and surfactants, from C16 to C22-rich natural oils such as soybean oil or palm oil. Soybean oil and palm oil can be more economical than, for example, coconut oil, which is a traditional starting material for making detergents. Cross-metathesis of unsaturated fatty esters with olefins generates new olefins and new unsaturated esters that can have reduced chain length and that may be difficult to make otherwise. Despite the availability of unsaturated fatty esters having reduced chain length, fatty N,N-dialkylamides made from these feedstocks are not yet widely available.
Recently, we described new compositions made from feedstocks based on self-metathesis of natural oils or cross-metathesis of natural oils and olefins. Among other compositions, we identified certain monounsaturated fatty amides made by derivatizing the unique feedstocks (see PCT Int. Publ. No. WO 2012/061094). The monounsaturated fatty amides showed outstanding performance as solvents for non-aqueous degreasers. Also exemplified were water-diluted samples containing 5 wt. % of the unsaturated N,N-dialkylamide and 10 wt. % of an amine oxide surfactant. Performance was superior compared with Steposol® M-8-10, a commercially available saturated fatty amide mixture. There is no suggestion to formulate a household hard surface cleaner, which normally has 5 wt. % or less of surfactants, and no mention of formulation pH.
We also recently demonstrated that many derivatives made from metathesis-based feedstocks have value for aqueous hard surface cleaners and industrial degreasers (see PCT Int. Publ. No. WO 2012/061103). In the '103 publication, we observed that the fatty N,N-dialkylamides are excellent as non-aqueous degreasers. In fact, the N,N-dialkylamides outperformed all of the other classes of compositions tested as potential industrial degreasers (see pp. 64-65). Although many classes of compounds were tested in aqueous hard surface cleaners, the N,N-dialkylamides were not evaluated.
Improved aqueous hard surface cleaners are always in demand. A valuable cleaner would perform well to remove greasy dirt, including baked-on soils. Ideally, the cleaner would work at a relatively neutral pH within the range of 6 to 9 to enable the formulation of low-alkalinity household cleaners for improved safety during use.